The present disclosure relates to a developing device that feeds developer to an image carrying member, and to an electrophotographic image forming apparatus provided with such a developing device.
In image forming apparatuses utilizing electrophotography, an electrostatic latent image is formed by irradiating the circumferential surface of an image carrying member (photosensitive drum) with light based on image data read from a document image or image data transmitted from an external device such as a computer. To this electrostatic latent image, toner is fed from a developing device to form a toner image, and then the toner image is transferred to a sheet. After the transfer, the sheet undergoes toner image fixing, and is then discharged to the outside.
As a developing system that uses dry toner adopted in image forming apparatuses adopting an electro-photographic process, a two-component developing system as will be described below that uses a magnetic roller (toner feeding roller) and a developing roller has been proposed. First, two-component developer is carried on a magnetic roller and then, while magnetic carrier is left on the magnetic roller, only non-magnetic toner is transferred to a developing roller to form a thin layer of toner thereon. Then, in a region (developing region) where the developing roller and a photosensitive member (image carrying member) face each other, by the action of an AC electric field, toner on the developing roller is made to fly to attach to an electrostatic latent image on the photosensitive member.
On the other hand, the recent ever-increasing speed of image formation in image forming apparatuses necessitates high-speed rotation of a toner stirring member in a developing device. In particular, with the above-mentioned developing system which uses two-component developer containing magnetic carrier and toner and which uses a magnetic roller carrying thereon developer and a developing roller carrying thereon toner alone, in the part where the developing roller and the magnetic roller face each other, toner alone flies from the magnetic roller to the developing roller, and in addition toner left unused during development flies from the developing roller to the magnetic roller. Thus, toner is likely to be suspended near the part where the developing roller and the magnetic roller face each other, and the suspended toner accumulates around a trimming blade (regulating blade). If the accumulated toner agglomerates and attaches to the developing roller, toner droppings may inconveniently result, leading to image defects.
As a solution to the inconvenience discussed above, a developing device is known which has an inner wall part facing a developing roller between a regulating blade and a developing region and which includes a film member that is arranged with a predetermined distance from a top surface of the inner wall part and that can vibrate in a direction approaching or away from the inner wall part, a biasing member which applies a tension to the film member, and an idle gear which constitutes a gear train driving the developing roller or the magnetic roller and which has formed thereon a protrusion that vibrates the film member by intermittently making contact with an edge of the film member as a gear rotates, wherein the film member is vibrated by the rotation of the idle gear to shake off the toner accumulated on the top surface of the inner wall part.